1. Field of Invention
The present invention relates to a display apparatus. More particularly, the present invention relates to an image display method for adjusting image size.
2. Description of Related Art
At present, most of the portable consumer devices are at least equipped with a LCD (Liquid Crystal Display). When user views contiguous images, since human vision system can adapt to and adjust itself to the quickly updated frames, therefore displays usually operate at a frame rate of more than 25 frames/second. If the frame rate is lower than 25 frames/second, user will see flickering images when viewing contiguous images.
In the current digital display systems, the frame rate is usually higher than 50 frames/second. In fact, a rate of 25 frames/second is enough for users to view contiguous images. Therefore this nature characteristic of human eyes can be used to develop an image size adjusting device which provides preferred viewing quality without using the line buffers. The Line buffer is used to maintain a series of image rows to perform high level real time vertical image adjustment. However, since some SRAMs (Static Random Access Memory) are required to maintain each row of pixels in LCD arrays, therefore the line buffer usually takes the cost of occupying a portion of silicon area. In order to save the memory space used by the line buffers, a known simple line-duplicate or line-drop technology is used to adjust (enlarge or reduce) image vertical size. However, such known technology may result in low image quality.
FIG. 1 schematically illustrates a known digital camera capturing system. Under image capture mode, the reflection light from a subject travels through a lens module 10, and the image sensor 11 converts the reflection into electronic image signals to depict the image of the subject. An image signal processor 12 receives and saves the electronic image signals into DRAM (Dynamic Random Access Memory) 13. In addition, the image signal processor 12 can also process the electronic image signals depending on the system requirement, and the processed electronic image signals are saved in memory 14. Before the digital camera captures image, a display panel 15 is used to preview the image of the subject. After digital camera captured and saved the electronic image signals in DRAM 13, digital camera can switch from capture mode to play mode to view the captured image of the subject. Under the play mode, the electronic image signals stored in DRAM 13 can be read out by an image signal processor 12 which enlarges or reduces the image size to fit in the size of display panel 15.
More specifically, since the size of original image depicted by the electronic image signals is not necessary the same size with the display panel 15, therefore the electronic image signals need to be processed to adjust the size of the original image. If the size of the original image is larger than the size of the display panel 15, then the size of the original image need to be reduced. When the image signal processor 12 adjusts the image vertical size bases on the known simple line-duplicate or line drop technology, an image distortion may occur.
For example, with reference to FIG. 2a and FIG. 2b, the original image 20 in FIG. 2a is reduced by half to form the image 21 in FIG. 2b. It can be seen from FIG. 2a and FIG. 2b, a portion of the image rows of the original image 20 are ignored and the characteristic of which doesn't show on image 21, especially for the characteristic of the upper half. Similarly, in FIG. 3a and FIG. 3b, the original image 30 of FIG. 3a is reduced by half to form the image 31 in FIG. 3b. It can be seen from FIG. 3a and FIG. 3b, a portion of image rows of the original image 30 was omitted. As a result, comparing with the original image 30, image 31 was totally distorted. Next with reference to FIG. 4a and FIG. 4b, the original image 40 is enlarged by one and half times (3/2 times) to form the image 41 in FIG. 4b. It can be seen from FIG. 4a and FIG. 4b, a portion of image rows of original image 40 was duplicated and a serrated edge was resulted.
Therefore the present invention provides an image display method which provides a resized image with preferred viewing quality through controlling image rows selection without using line buffer.